Ways to Prevent Pump-Around Heat Exchanger Fouling and Extend Run Lengths on a Benzene Hydrogenation Unit

ABSTRACT

A process for hydrogenation of an aromatic hydrocarbon including introducing a hydrocarbon feed comprising the aromatic hydrocarbon, a hydrogen feed comprising hydrogen, and a hydrogenation catalyst into a hydrogenation reactor operable with a liquid phase and a gas phase to produce a hydrogenation product; removing a gas phase product stream comprising the hydrogenation product; withdrawing a portion of the liquid phase; subjecting the withdrawn portion to heat exchange to provide a reduced-temperature withdrawn portion; introducing the reduced-temperature withdrawn portion back into the hydrogenation reactor; and at least one of: (a) providing at least two heat exchangers to effect the subjecting of the withdrawn portion of the liquid phase to heat exchange; (b) separating a decomposition product of the hydrogenation catalyst, the hydrogenation catalyst, or both, from the withdrawn portion of the liquid phase prior to the heat exchange; and (c) reducing exposure of the hydrogenation catalyst to an oxygen-containing species.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

TECHNICAL FIELD

This disclosure relates to the hydrogenation of aromatic hydrocarbons;still more specifically, this disclosure relates to a system and methodfor liquid phase hydrogenation of aromatic hydrocarbons; even morespecifically, this disclosure relates to the liquid phase hydrogenationof benzene to produce cyclohexane.

BACKGROUND

Cyclohexane is currently produced using a liquid phase benzenehydrogenation reactor. As the hydrogenation reaction is quiteexothermic, heat must be continuously removed from the system. Heatremoval is primarily effected via a pump-around loop, via whichwithdrawn reactor liquid phase is continuously moved through a heatexchanger in which it is cooled. The heat exchanger often operates toproduce low pressure steam. The cooled liquid is returned to thehydrogenation reactor. Fresh catalyst may be added to this cooled liquidprior to reintroduction into the hydrogenation reactor.

Undesirably, the catalyst may gradually plate out on the heat exchanger,resulting in reduced performance of the heat exchanger, and eventually aneed to shut the plant down. The decrease in run life and concomitantincrease in the number of turnarounds is uneconomical and detrimental tothe overall unit economics.

An ongoing need thus exists for a system and process that reduce oreliminate heat exchanger fouling during the hydrogenation of aromatichydrocarbon(s), and/or allow for cleaning of the heat exchanger withouthalting production.

SUMMARY

Disclosed herein is a process for liquid phase hydrogenation of anaromatic hydrocarbon, the process comprising: introducing a hydrocarbonfeed comprising the aromatic hydrocarbon, a hydrogen feed comprisinghydrogen, and a hydrogenation catalyst into a hydrogenation reactoroperable with a liquid phase and a gas phase, whereby at least a portionof the aromatic hydrocarbon is hydrogenated to produce a hydrogenationproduct; removing, from the hydrogenation reactor, a gas phase productstream comprising the hydrogenation product; withdrawing, from thehydrogenation reactor, a portion of the liquid phase; subjecting atleast a portion of the withdrawn portion of the liquid phase to heatexchange, thus providing a reduced-temperature withdrawn portion;introducing the reduced-temperature withdrawn portion back into thehydrogenation reactor; and at least one of: (a) providing at least twoheat exchangers to effect the subjecting of the withdrawn portion of theliquid phase to heat exchange, such that a first heat exchanger of theat least two heat exchangers can be online while a second heat exchangerof the at least two heat exchangers is offline; (b) separating adecomposition product of the hydrogenation catalyst, the hydrogenationcatalyst, or both, from the withdrawn portion of the liquid phase priorto subjecting the at least a portion of the withdrawn portion of theliquid phase to heat exchange; and (c) reducing exposure of thehydrogenation catalyst to an oxygen-containing species.

Also disclosed herein is a system for liquid phase hydrogenation, thesystem comprising: a hydrogenation reactor operable with a liquid phaseand a gas phase to convert an aromatic hydrocarbon in a hydrocarbon feedto a hydrogenation product by contacting the aromatic hydrocarbon withhydrogen in a hydrogen feed in the presence of a hydrogenation catalyst;a pump-around loop comprising a pump configured to move a withdrawnportion of the liquid phase from the hydrogenation reactor through thepump-around loop and back to the hydrogenation reactor; at least oneprimary heat exchanger after the pump in the pump-around loop andconfigured to reduce the temperature of at least a portion of the liquidphase withdrawn from the hydrogenation reactor, thus providing areduced-temperature withdrawn portion, prior to introduction of thereduced-temperature withdrawn portion into the hydrogenation reactor;and at least one of: (a) at least one additional heat exchanger inparallel with the at least one primary heat exchanger, and configuredsuch that the at least one primary heat exchanger can be placed offlinewhile the at least one additional heat exchanger is placed online; (b) aseparator upstream of the at least one primary heat exchanger, andconfigured to separate a decomposition product of the hydrogenationcatalyst, the hydrogenation catalyst, or both from the withdrawn portionof the liquid phase; and (c) a dryer operable to dry the hydrocarbonfeed, the hydrogen feed, both the hydrocarbon feed and the hydrogenfeed, or a mixture of the hydrocarbon feed and the hydrogen feed; asource of a component that will react with an oxygen-containing speciesin the hydrocarbon feed, the hydrogen feed, or both; or both the dryerand the source of the component.

Also disclosed herein is a process for hydrogenation of benzene tocyclohexane, the process comprising: introducing a benzene feedcomprising benzene, a hydrogen feed comprising hydrogen, and ahydrogenation catalyst comprising nickel into a hydrogenation reactoroperable with a liquid phase and a gas phase, whereby at least a portionof the benzene is hydrogenated to produce cyclohexane; removing from thehydrogenation reactor a gas phase product stream comprising cyclohexane;withdrawing from the liquid phase a pump-around stream from the reactor;passing at least a portion of the pump-around stream to a heat exchangerbank comprising at least a first heat exchanger in parallel with asecond heat exchanger such that the first heat exchanger can be onlinewhile the second heat exchanger is offline, and vice versa; cooling theat least a portion of the pump-around stream in the heat exchanger bankto provide a reduced-temperature pump-around stream; and introducing thereduced-temperature pump-around stream back into the hydrogenationreactor.

Also disclosed herein is a process for hydrogenation of benzene tocyclohexane, the process comprising: introducing a benzene feedcomprising benzene, a hydrogen feed comprising hydrogen, and ahydrogenation catalyst slurry comprising a supported nickel catalystinto a hydrogenation reactor operable with a liquid phase and a gasphase, whereby at least a portion of the benzene is hydrogenated toproduce cyclohexane; removing a product stream comprising cyclohexanefrom the gas phase of the hydrogenation reactor; withdrawing apump-around stream from the liquid phase of the hydrogenation reactor,wherein the pump-around stream comprises supported nickel catalyst;separating the supported nickel catalyst from the pump-around stream toproduce a supported nickel catalyst stream and a substantiallycatalyst-free pump-around stream; passing at least a portion of thesubstantially catalyst-free pump-around stream to a heat exchanger;cooling the at least a portion of the substantially catalyst-freepump-around stream in the heat exchanger to provide areduced-temperature pump-around stream; and introducing thereduced-temperature pump-around stream and at least a portion of thesupported nickel catalyst stream back into the hydrogenation reactor.

Also disclosed herein is a process for hydrogenation of benzene tocyclohexane, the process comprising: treating a benzene feed comprisingbenzene to form a treated benzene feed, treating a hydrogen feedcomprising hydrogen to form a treated hydrogen feed, both treating abenzene feed comprising benzene to form a treated benzene feed andtreating a hydrogen feed comprising hydrogen to form a treated hydrogenfeed, or treating a mixed feed comprising benzene and hydrogen to form atreated mixed feed, wherein treating reduces an amount ofoxygen-containing species therein, wherein the oxygen containing speciescomprise carbon monoxide, carbon dioxide, oxygen, water, or acombination thereof; introducing the treated benzene feed, the treatedhydrogen feed, both the treated benzene feed and the treated hydrogenfeed, or the treated mixed feed, and a hydrogenation catalyst comprisingnickel and at least one aluminum alkyl into a hydrogenation reactoroperable with a liquid phase and a gas phase, whereby at least a portionof the benzene is hydrogenated to produce cyclohexane; removing aproduct stream comprising cyclohexane from the gas phase of thehydrogenation reactor; withdrawing a pump-around stream from the liquidphase of the hydrogenation reactor; passing at least a portion of theliquid phase pump-around stream to a heat exchanger; cooling the atleast a portion of the liquid phase pump-around stream in the heatexchanger to provide a reduced-temperature pump-around stream, andintroducing the reduced-temperature pump-around stream back into thehydrogenation reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description will reference the drawings briefly describedbelow, wherein like reference numerals represent like parts, unlessotherwise indicated.

FIG. 1 is a schematic of a liquid phase hydrogenation system whichutilizes two substantially equivalent heat exchangers, according to anembodiment of this disclosure;

FIG. 2 is a schematic of a liquid phase hydrogenation system whichutilizes two disparate heat exchangers, according to another embodimentof this disclosure;

FIG. 3 is a schematic of a liquid phase hydrogenation system whichutilizes removal of catalyst, according to another embodiment of thisdisclosure; and

FIG. 4 is a schematic of a liquid phase hydrogenation system whichutilizes addition of aluminum alkyls, according to another embodiment ofthis disclosure.

DETAILED DESCRIPTION

Herein disclosed are systems and methods for hydrogenation of aromatichydrocarbon(s). Although described with reference to the hydrogenationof benzene to produce cyclohexane, it is to be understood that theherein-disclosed system and method are likewise suitable for thehydrogenation of other aromatic hydrocarbons as well. The disclosedsystem and method provide for increased run length by reducing orsubstantially preventing the deposition of catalyst and/or catalystdecomposition products on a pump-around heat exchanger, and/or enablingcontinuous operation during cleaning of a pump around heat exchanger.Such systems and methods may thus provide for enhanced run lengths, andthe concomitant savings on turnarounds.

The herein-disclosed system and process may enable or compriseintroducing a hydrocarbon feed comprising the aromatic hydrocarbon, ahydrogen feed comprising hydrogen, and a hydrogenation catalyst into ahydrogenation reactor operable with a liquid phase and a gas phase,whereby at least a portion of the aromatic hydrocarbon is hydrogenatedto produce a hydrogenation product; removing a gas phase product streamcomprising the hydrogenation product from the hydrogenation reactor;withdrawing a portion of the liquid phase, subjecting at least a portionof the withdrawn portion of the reactor liquid phase to heat exchange,thus providing a reduced-temperature withdrawn portion, introducing thereduced-temperature withdrawn portion back into the hydrogenationreactor; and at least one of: (a) providing at least two heat exchangersto effect the subjecting of the withdrawn portion of the liquid phase toheat exchange, such that a first heat exchanger of the at least two heatexchangers can be online while a second heat exchanger of the at leasttwo heat exchangers is offline; (b) separating a decomposition productof the hydrogenation catalyst, the hydrogenation catalyst, or both, fromthe withdrawn portion of the liquid phase prior to subjecting the atleast a portion of the withdrawn portion of the liquid phase to heatexchange; (c) reducing exposure of the hydrogenation catalyst to anoxygen-containing species; or (d) combinations thereof.

In embodiments, shut-down of the hydrogenation unit is made unnecessaryby adding a second heat exchanger, according to (a), which may beutilized while the other heat exchanger is being cleaned, such that thehydrogenation unit remains operating during the cleaning. Inembodiments, the first (or primary) heat exchanger and the second heatexchanger are substantially identical. In embodiments, the second heatexchanger is smaller than the first or primary heat exchanger. The firstheat exchanger and the second heat exchanger may operate with coolingmedia having different compositions, may operate with different inlettemperatures, or both. In embodiments, the cooling medium of the firstor primary heat exchanger is boiler feed water and low pressure steam isproduced therein, and the cooling medium of the second heat exchanger isselected from the group consisting of cooling water and refrigerants.

In embodiments, catalyst deposition on the heat exchanger is preventedor minimized via (b). In such embodiments, solid decomposition productsof the hydrogenation catalyst, or a solid hydrogenation catalyst, orboth, may be separated prior to the heat exchange. In some suchembodiments, a supported catalyst is employed, with the hydrogenationbeing operated as a slurry, and the supported catalyst is separated fromthe withdrawn liquid phase upstream or downstream of a pump of thepump-around loop, whereby solids can be removed upstream of the heatexchanger. In embodiments, separating hydrogenation catalyst and/ordecomposition product thereof from the withdrawn portion of the liquidphase comprises introducing the withdrawn portion of the liquid phaseinto a cyclone. The withdrawn portion of the liquid phase may be pumpedinto at least one heat exchanger via a pump, and the cyclone may beupstream of the pump or it may be downstream of the pump. At least aportion of the separated hydrogenation catalyst can be reintroduced intothe hydrogenation reactor. At least a portion of the separatedhydrogenation catalyst and/or of the separated decomposition product ofthe hydrogenation catalyst may be purged. In embodiments, thehydrogenation catalyst further comprises a support. In embodiments, thesupport comprises at least one component selected from the groupconsisting of silica, alumina, and carbon.

In embodiments, run length may be increased by (c), by selectivelyremoving oxygen-containing species, such as, without limitation, carbonmonoxide, carbon dioxide, oxygen, and water, from the feed and/or fromthe hydrogenation reactor. Selectively removing oxygen-containingspecies may comprise drying the hydrocarbon feed, the hydrogen feed, orboth (i.e., drying both the hydrogen feed and the hydrocarbon feedseparately, or drying a mixed feed containing both the hydrocarbon feedand the hydrogen feed) prior to introducing same into the hydrogenationreactor, and/or adding a component to the hydrocarbon feed, the hydrogenfeed, or both (i.e., adding the component to both the hydrogen feed andthe hydrocarbon feed separately, or adding the component to a mixed feedcontaining both the hydrocarbon feed and the hydrogen feed), wherein thecomponent is a compound that will react with the oxygen-containingspecies. The compound may be selected from the group consisting ofaluminum alkyls. In embodiments, the hydrocarbon feed and the hydrogenfeed are combined to provide a combined or mixed feed prior tointroducing the combined or mixed feed into the hydrogenation reactor.In such embodiments, adding a component to the hydrocarbon feed, thehydrogen feed, or both may comprise adding the component to the combinedor mixed feed.

In embodiments, hydrogenation of an aromatic hydrocarbon is effected viaat least one step selected from the group consisting of (a) providing atleast two heat exchangers to effect the subjecting of the withdrawnportion of the liquid phase to heat exchange, (b) separating thehydrogenation catalyst, a decomposition product of the hydrogenationcatalyst, or both, from the withdrawn portion of the liquid phase priorto subjecting the withdrawn portion of the liquid phase to heatexchange, and (c) reducing exposure of the hydrogenation catalyst to anoxygen-containing species.

In embodiments, hydrogenation of an aromatic hydrocarbon is effected viaa combination of two or more steps selected from the group consisting of(a) providing at least two heat exchangers to effect the subjecting ofthe withdrawn portion of the liquid phase to heat exchange, (b)separating the hydrogenation catalyst, a decomposition product of thehydrogenation catalyst, or both, from the withdrawn portion of theliquid phase prior to subjecting the withdrawn portion of the liquidphase to heat exchange, and (c) reducing exposure of the hydrogenationcatalyst to an oxygen-containing species.

Herein disclosed is a system operable for the hydrogenation of aromatichydrocarbon(s). A system for liquid phase hydrogenation according tothis disclosure comprises a hydrogenation reactor operable with a liquidphase and a gas phase to convert an aromatic hydrocarbon in ahydrocarbon feed to a hydrogenation product by contacting the aromatichydrocarbon with hydrogen in a hydrogen feed in the presence of ahydrogenation catalyst; a pump-around loop comprising a pump configuredto move a withdrawn portion of the liquid phase from the hydrogenationreactor through the pump-around loop and back to the hydrogenationreactor; at least one primary heat exchanger after the pump in thepump-around loop and configured to reduce the temperature of at least aportion of the liquid phase withdrawn from the hydrogenation reactor,thus providing a reduced-temperature withdrawn portion, prior tointroduction of the reduced-temperature withdrawn portion back into thehydrogenation reactor; and at least one of: (a) at least one additionalheat exchanger in parallel with the at least one primary heat exchanger,and configured such that the at least one primary heat exchanger can beplaced offline while the at least one additional heat exchanger isplaced online; (b) a separator upstream of the at least one primary heatexchanger, and configured to separate the hydrogenation catalyst, adecomposition product of the hydrogenation catalyst, or both, from thewithdrawn portion of the liquid phase; (c) a dryer operable to dry thehydrocarbon feed, the hydrogen feed, both the hydrocarbon feed and thehydrogen feed, or a mixture of the hydrocarbon feed and the hydrogenfeed; a source of a component that will react with an oxygen-containingspecies in the hydrocarbon feed, the hydrogen feed, or both; or both thedryer and the source of the component; or (d) combinations thereof.

In embodiments, therefore, a hydrogenation system of this disclosurecomprises (a), at least one additional heat exchanger in parallel withthe at least one primary heat exchanger, and configured such that the atleast one primary heat exchanger can be placed offline while the atleast one additional heat exchanger is placed online. Description ofsuch a hydrogenation system will now be made with reference to FIG. 1,which is a schematic of a hydrogenation system 100, according to anembodiment of this disclosure, which utilizes two substantially equalheat exchangers. Hydrogenation system 100 comprises hydrogenationreactor 120, pump 130, first (or ‘primary’) heat exchanger 140A, andsecond (or additional) heat exchanger 140B. Liquid phase hydrogenationsystem 100 is operable such that first heat exchanger 140A can be placedonline while second heat exchanger 140B can be placed offline, and viceversa. Via this arrangement, hydrogenation reactor 120 can be keptonline while one of the heat exchangers 140A/B is cleaned or serviced,by placing the other of the heat exchangers 140A/B into service whileremoving from service the heat exchanger that is fouled or otherwise inneed of service or maintenance.

In embodiments, at least one heat exchanger is configured to produce lowpressure steam. In embodiments, first heat exchanger 140A and secondheat exchanger 140B are substantially identical. In embodiments, such asthat of FIG. 1, first heat exchanger 140A and second heat exchanger 140Bare substantially the same size. Hydrocarbon feed line 105 is fluidlyconnected with hydrogenation reactor 120, and configured for theintroduction of hydrocarbon feed thereto. A hydrogen feed line 115 isfluidly connected with hydrogenation reactor 120, and configured for theintroduction of gas containing hydrogen thereto. Reactor liquid phaseoutlet line 125 fluidly connects hydrogenation reactor 120 with pump130, whereby a portion of the reactor liquid withdrawn from the liquidphase within hydrogenation reactor 120 can be introduced into pump 130.Pump 130 is fluidly connected with first heat exchanger 140A via pumpoutlet line 135A, and with second heat exchanger 140B via pump outletline 135B. Heat exchangers 140A/140B are configured to reduce thetemperature of the reactor liquid introduced thereto, via heat exchangewith a heat exchange fluid in heat transfer line 145A/145B,respectively. First heat exchanger outlet line 150A fluidly connectsfirst heat exchanger 140A with hydrogenation reactor 120 via recycleline 165, whereby a cooled withdrawn portion of the liquid phase can bereintroduced into hydrogenation reactor 120; second heat exchangeroutlet line 150B fluidly connects second heat exchanger 140B withhydrogenation reactor 120 via recycle line 165, whereby cooled withdrawnliquid phase can be reintroduced into hydrogenation reactor 120. A gasphase hydrogenation product outlet line 155 is fluidly connected withhydrogenation reactor 120, and configured for the removal of gas phasehydrogenation product therefrom. A fresh catalyst inlet line 160 isconfigured to introduce catalyst into hydrogenation reactor 120, forexample, via recycle line 165. Valves V1 and V2 are operable to directflow within the pump-around loop to first heat exchanger 140A or secondheat exchanger 140B, respectively.

In embodiments, the first heat exchanger and the second heat exchangerare substantially the same size and operate with the same cooling medium(e.g., boiler feed water for production of low pressure steam) inrespective heat transfer lines thereof, and/or operate with coolingmedia having the same inlet temperatures.

In embodiments, the first heat exchanger and the second heat exchangerare substantially the same size, but operate with a different coolingmedium (e.g., boiler feed water for production of low pressure steam incontrast to cooled or chilled water, for example from an ambientevaporative cooling tower) in respective heat transfer lines thereof,and/or operate with cooling media having differing inlet temperatures.

In embodiments, the first heat exchanger and the second heat exchangerare of different sizes. Such an embodiment is depicted in FIG. 2, whichis a schematic of a hydrogenation system 200, according to anotherembodiment of this disclosure which utilizes two heat exchangers, one ofwhich is a smaller swing heat exchanger operable with a differentcooling medium than that with which the other heat exchanger operates.In this embodiment, first heat exchanger 240A is larger than second or‘additional’ heat exchanger 240B, and first heat exchanger 240A is aprimary heat exchanger that is utilized except in situations where sameneeds cleaning or maintenance. In embodiments, second heat exchanger240B is a smaller ‘swing’ heat exchanger, which may allow for capitalsavings. In such embodiments, the heat throughput of second heatexchanger 240B may be increased and/or the reaction rate decreased,which may be acceptable providing the time needed to clean or otherwiseservice the primary heat exchanger is sufficiently brief. The heatthroughput of second heat exchanger 240B may be increased viautilization of a different cooling medium therein, such as, withoutlimitation, cooling water or refrigerant in contrast to water (e.g.,boiler feed water) yielding low pressure steam. In this manner, secondheat exchanger 240B may be operable to cool the reactor liquidintroduced thereto to a greater extent, thus enabling substantiallyequivalent heat removal as provided by first heat exchanger 240A, with alower flow rate. Thus, in embodiments, heat transfer line 245Bintroduces cooling water or refrigerant into second heat exchanger 240B.In embodiments, primary heat exchanger 240A is configured to produce lowpressure steam in heat transfer line 245A. Thus, in embodiments, heattransfer line 245A introduces boiler feed water into and removes lowpressure steam from first heat exchanger 240A. In such embodiments,utilization of a smaller ‘swing’ heat exchanger as second heat exchanger240B may not enable the production of low pressure steam generationwhile primary heat exchanger 240A is being serviced.

System 200 comprises hydrogenation reactor 220, pump 230, hydrocarbonfeed line 205, hydrogen feed line 215, reactor liquid phase outlet line225, gas phase hydrogenation product outlet line 255, pump outlet lines235A and 235B, first heat exchanger outlet line 250A and second heatexchanger outlet line 250B, fresh catalyst inlet line 260, and recycleline 265, which correspond with hydrogenation reactor 120, pump 130,hydrocarbon feed line 105, hydrogen feed line 115, reactor liquid phaseoutlet line 125, gas phase hydrogenation product outlet line 155, pumpoutlet lines 135A and 135B, first heat exchanger outlet line 150A andsecond heat exchanger outlet line 150B, fresh catalyst inlet line 160,and recycle line 165 of the embodiment of FIG. 1.

As noted hereinabove, in embodiments, a hydrogenation system accordingto this disclosure comprises (b) a separator upstream of the at leastone primary heat exchanger, and configured to separate hydrogenationcatalyst, a decomposition product of the hydrogenation catalyst, orboth, from the withdrawn portion of the reactor liquid phase.Description of such a hydrogenation system will now be made withreference to FIG. 3, which is a schematic of a hydrogenation system,according to another embodiment of this disclosure, which utilizesremoval of catalyst upstream of the heat exchange to enhance run length.Hydrogenation system 300 comprises hydrogenation reactor 320, pump 330,separator 370, and heat exchanger 340. Hydrogenation system 300 isoperable such that the heat exchanger 340 is not exposed to thehydrogenation catalyst and/or solid decomposition products thereof (orsuch exposure is reduced/minimized), which thus prevents (or at leastreduces/minimizes) plating out and/or accumulation of catalystcomponent(s) (e.g., nickel) and/or decomposition products thereof (e.g.,nickel deposits) on the heat exchanger surfaces. In some suchembodiments, the catalyst is supported, and the hydrogenation reactioncarried out as a slurry phase.

Hydrogenation system 300 comprises reactor liquid phase outlet line 325,which is operable to withdraw reactor liquid from the liquid phasewithin hydrogenation reactor 320. In embodiments, reactor liquid phaseoutlet line 325 fluidly connects hydrogenation reactor 320 withseparator 370, whereby reactor liquid withdrawn via reactor liquid phaseoutlet line 325 is introduced into separator 370. Separator 370 may beany separator operable for solid/liquid separation, whereby solidcatalyst and/or solid catalyst decomposition product(s) (collectively,“solids”) may be separated from the reactor liquid phase introducedthereto. In embodiments, separator 370 comprises a solid/liquidseparation device selected from cyclones, filters, gravitationalsettling chambers, and combinations thereof. In embodiments, separator370 is operable for on-stream cleaning. In other embodiments, aseparator 370, such as, for example, a spent catalyst drum, is operablefor off-stream separation of spent catalyst. In embodiments, separator370 comprises a centrifugal force separator such as a cyclone. Aseparator liquid outlet line 395 may fluidly connect separator 370 withpump 330, which is configured to pump reactor liquid from which solidshave been removed into heat exchanger 340, via pump outlet line 335. Aseparator solids outlet line 380 is configured for the removal of solidsfrom separator 370. A solids return line 390 may be configured toreintroduce solids separated from the withdrawn reactor liquid phaseback into hydrogenation reactor 320. In embodiments, a purge line 385 isconfigured to remove a portion of the separated solid particles (e.g.,solid catalyst particles and/or solid catalyst decomposition product(s))from system 300. Such purge may be utilized, in embodiments, to maintaina desired catalyst inventory within hydrogenation reactor 320 by, forexample, balancing catalyst purge via purge line 385 and introduction offresh catalyst via fresh catalyst inlet line 360. In this manner,catalyst buildup in system 300 can be avoided.

As noted by dashed line 375 in FIG. 3, separator 370 may, inembodiments, be positioned downstream of pump 330. Thus, separator 370may be located either upstream or downstream of pump 330.

As noted hereinabove, in embodiments in which run length is increasedvia separation/removal of solids upstream of a heat exchanger of thepump-around loop, the catalyst can be a supported catalyst. In suchembodiments, the catalyst support may be any hydrogenation catalystsupport known to those of skill in the art. For example, in embodiments,the catalyst comprises a support selected from silica, alumina, carbon,and combinations thereof.

Hydrocarbon feed line 305 is fluidly connected with hydrogenationreactor 320, and configured for the introduction of hydrocarbon feedcomprising an aromatic hydrocarbon to be hydrogenated thereto. Ahydrogen feed line 315 is fluidly connected with hydrogenation reactor320, and configured for the introduction of gas containing hydrogenthereto. As discussed in detail above, reactor liquid phase outlet line325 fluidly connects hydrogenation reactor 320 with pump 330 orseparator 370 (depending on whether separator 370 is positioned upstreamor downstream of pump 330), whereby reactor liquid phase withdrawn fromhydrogenation reactor 320 can be introduced into pump 330 or separator370. Pump 330 or separator 370 is fluidly connected with heat exchanger340 via pump outlet line 335 or separator liquid outlet line 395. Heatexchanger 340 is configured to reduce the temperature of the reactorliquid phase introduced thereto, via heat exchange with a heat exchangefluid in heat transfer line 345. Heat exchanger outlet line 350 fluidlyconnects heat exchanger 340 with hydrogenation reactor 320 via recycleline 365, whereby cooled reactor liquid phase can be reintroduced intohydrogenation reactor 320. A gas phase hydrogenation product outlet line355 is fluidly connected with hydrogenation reactor 320, and configuredfor the removal of gaseous hydrogenation product therefrom. A freshcatalyst inlet line 360 is configured to introduce catalyst intohydrogenation reactor 320, for example, via heat exchanger recycle line365.

As noted hereinabove, in embodiments, a hydrogenation system accordingto this disclosure comprises apparatus configured for reducing exposureof the hydrogenation catalyst to oxygen-containing species. Suchapparatus may comprise (i) a dryer operable to dry the hydrocarbon feed,the hydrogen feed, or both (i.e., to dry the hydrocarbon feed and thehydrogen feed separately, or dry a mixed feed containing the hydrocarbonfeed and the hydrogen feed); (ii) a source of a component that willreact with oxygen-containing species in the hydrocarbon feed, thehydrogen feed, or both; or (iii) both a dryer and a source of thecomponent that will react with oxygen-containing species. Inembodiments, a hydrogenation system of this disclosure comprises a dryerconfigured to dry the hydrocarbon feed, the hydrogen feed, both thehydrocarbon feed and the hydrogen, or a combined or mixed feed streamcomprising the hydrocarbon feed and the hydrogen feed.

Description of a hydrogenation system comprising apparatus configuredfor reducing exposure of the hydrogenation catalyst to reactive (e.g.,oxygen-containing) species will now be made with reference to FIG. 4,which is a schematic of a hydrogenation system 400, according to anotherembodiment of this disclosure, which utilizes addition of a componentfrom a source of the component to enhance run length. Hydrogenationsystem 400 comprises hydrogenation reactor 420, pump 430, and heatexchanger 440. Hydrogenation system 400 is operable such that the levelof oxygen-containing species (e.g., carbon monoxide, carbon dioxide,oxygen, water, and the like), in the hydrocarbon feed introduced viahydrocarbon feed line 405 and/or in hydrogen feed introduced viahydrogen feed line 415 is reduced. Reduction of such oxygen-containingspecies is desirable, as the presence of such species encourages theplating out of catalyst component(s) (e.g., nickel) on the heatexchanger surfaces. In embodiments, a hydrogenation system of thisdisclosure comprises a dryer 475 configured to dry the hydrocarbon feed,the hydrogen feed, or both (separately, or combined), whereby the levelof oxygen-containing species (e.g., water) can be reduced. Inembodiments, such a dryer is utilized in conjunction with a source of acomponent that will react with oxygen-containing species in thehydrocarbon feed, the hydrogen feed, or both. Selectively removing suchoxygen-containing species from the reactor or reactor feed(s) may thusprovide for enhanced run length, by reducing or preventing plating outof catalyst component(s) and/or decomposition products on the surfacesof the heat exchanger(s).

In the embodiment of FIG. 4, hydrogenation system 400 comprises a sourceof a component that will react with oxygen-containing species in thehydrocarbon feed, the hydrogen feed, or both. The source of thecomponent comprises component feed line 406, which is configured tointroduce a component that will react with oxygen-containing speciesinto hydrocarbon feed line 405. In embodiments, the source of thecomponent (e.g., component feed line 406) is fluidly connected withhydrogen feed line 415, whereby the component that will react withoxygen-containing species is introduced into the hydrogen feed. Inembodiments, one or more source of the component (e.g., component feedline 406) is fluidly connected with (a) hydrogen feed line 415, wherebythe component that will react with oxygen-containing species isintroduced into the hydrogen feed, and (b) with hydrocarbon feed line405, whereby the component that will react with oxygen-containingspecies can also be introduced into the hydrocarbon feed. Inembodiments, hydrogenation system 400 comprises piping whereby thehydrocarbon feed and the hydrogen feed can be combined to provide acombined or mixed feed prior to introduction of the combined or mixedfeed into hydrogenation reactor 420. Such a system may further comprisepiping whereby the component that will react with oxygen-containingspecies can be added via the source of the component (e.g., componentfeed line 406) to the combined feed.

Desirably, the component that will react with oxygen-containing speciesadded via the source of said component is a species that will quicklyreact with the oxygen-containing impurities, thus preventing orminimizing detrimental effects such species could have on thehydrogenation catalyst, and/or downstream equipment (e.g., the heatexchanger(s) of the pump-around loop). In embodiments, the componentthat will react with oxygen-containing species is selected from thegroup consisting of aluminum alkyls. The aluminum alkyl compound usedwith the present disclosure can have the formula: (R³)₃Al; in which (R³)is an aliphatic group having from 1 to about 6 carbon atoms. In someinstances, (R³) is methyl, ethyl, propyl, butyl, hexyl, or isobutyl. Inembodiments, the aluminum alkyl compound comprises an aluminum alkylhalide such as, but not limited to, diethylaluminum chloride (DEAC) ordimethylaluminum chloride (DMAC). Utilization of aluminum alkyls as thecomponent that will react with oxygen-containing species may beparticularly desirable in systems utilizing catalyst systems thatcomprise one or more aluminum alkyls, as addition of same would not beexpected to undesirably influence the overall reaction. In embodiments,the component that will react with oxygen-containing species is added ata molar ratio of aluminum alkyl to oxygen containing species of between1:3 and 3:1. In another embodiment, the specific amount can depend onthe amount of oxygen and moisture in the feed.

Hydrogenation system 400 further comprises reactor liquid phase outletline 425, which is operable to withdraw reactor liquid phase fromhydrogenation reactor 420. Reactor liquid phase outlet line 425 fluidlyconnects hydrogenation reactor 420 with pump 430, which is configured topump reactor liquid into heat exchanger 440, via pump outlet line 435.Hydrocarbon feed line 405 is fluidly connected with hydrogenationreactor 420, and configured for the introduction of hydrocarbon feedthereto. A hydrogen feed line 415 is fluidly connected withhydrogenation reactor 420, and configured for the introduction of gascontaining hydrogen thereto. Reactor liquid phase outlet line 425fluidly connects hydrogenation reactor 420 with pump 430, wherebyreactor liquid phase withdrawn from hydrogenation reactor 420 can beintroduced into pump 430. Pump 430 is fluidly connected with heatexchanger 440 via pump outlet line 435. Heat exchanger 440 is configuredto reduce the temperature of the reactor liquid introduced thereto, viaheat exchange with a heat exchange fluid in heat transfer line 445. Heatexchanger outlet line 450 fluidly connects heat exchanger 440 withhydrogenation reactor 420 via recycle line 465, whereby cooled withdrawnreactor liquid phase can be reintroduced into hydrogenation reactor 420.A gas phase hydrogenation product outlet line 455 is fluidly connectedwith hydrogenation reactor 420, and configured for the removal ofgaseous hydrogenation product therefrom. A fresh catalyst inlet line 460is configured to introduce catalyst into hydrogenation reactor 420, forexample, via heat exchanger recycle line 465.

The hydrogenation catalyst introduced via line(s) 160/260/360/460 is anyhydrogenation catalyst known to those of skill in the art to be operableto catalyze the desired hydrogenation reaction. In embodiments, thehydrogenation catalyst is a catalyst operable to catalyze the liquidphase hydrogenation of benzene to produce cyclohexane. Such catalyst maybe a catalyst known to those of skill in the art. In embodiments, thehydrogenation catalyst comprises soluble and/or colloidal nickel speciesand aluminum alkyls. In embodiments, the catalyst comprisestrialkylaluminum, nickel carboxylate, and sodium carboxylate in asaturated hydrocarbon solution, as described, for example, in U.S. Pat.No. 5,668,293, the disclosure of which is hereby incorporated herein forpurposes not contrary to this disclosure.

In embodiments, the catalyst comprises a metal from Group VIII of theperiodic table. In embodiments, the catalyst comprises nickel, platinum,palladium, iron, or a combination thereof. In embodiments, the catalystcomprises nickel. In embodiments, the hydrogenation catalyst comprisessoluble nickel species and one or more aluminum alkyls. In embodiments,the hydrogenation catalyst comprises a trialkylaluminum, nickelcarboxylate, and sodium carboxylate in a saturated hydrocarbon solutionas described, for example, in U.S. Pat. No. 5,668,293. In embodiments, ahomogeneous or soluble hydrogenation catalyst is employed. Inembodiments, the catalyst comprises a solid support. In embodiments, thecatalyst support is selected from silica, alumina, magnesia, carbon, andcombinations thereof.

Hydrogenation reactor 120/220/320/420 may be any hydrogenation reactoroperable for hydrogenation of hydrocarbons with a liquid phase and a gasphase. In embodiments, the hydrogenation reactor is operable with asoluble or homogeneous catalyst. In embodiments, the hydrogenationreactor is operable with a slurry phase of catalyst comprising acatalyst with a solid support. In embodiments, the hydrogenation reactoris not a fixed bed reactor. In embodiments, hydrogenation reactor120/220/320/420 is a continuous flow reactor with a pump around loop, asdescribed, for example, in U.S. Pat. No. 5,668,293.

In embodiments, the herein-disclosed hydrogenation system furthercomprises a finishing hydrogenation reactor downstream of hydrogenationreactor 120/220/320/420, and configured to hydrogenate unconvertedaromatic hydrocarbon in the gas phase hydrogenation product stream ingas phase hydrogenation product outlet line 155/255/355/455. Inembodiments, such a finishing reactor is operable with a solid catalyst.In embodiments, the finishing hydrogenation reactor is operable with afixed bed of hydrogenation catalyst, as described, for example, in U.S.Pat. No. 5,668,293.

Also disclosed herein is a method for liquid phase hydrogenation ofaromatic hydrocarbon(s). The disclosed method provides for hydrogenationof an aromatic hydrocarbon utilizing a hydrogenation reactor operatedwith a pump-around heat exchanger loop. Run length may be increased viathe disclosed method relative to conventional hydrogenation methods, byreducing or eliminating the deposition of hydrogenation catalystcomponent(s) and/or decomposition products on the surfaces of the heatexchanger and/or enabling heat exchanger cleaning while maintainingoperation of the hydrogenation system. Such reduction or elimination ofcatalyst deposition is provided in a number of ways, including one ormore of separating catalyst from the withdrawn reactor fluid upstream ofthe heat exchanger of the pump-around loop, whereby catalyst does notenter the heat exchanger; removing reactive species from thehydrogenation reactor and/or from the hydrogenation reactor feed(s) (forexample, via drying of the feed(s) and/or addition of a componentthereto that reacts with said reactive species); utilization of a secondheat exchanger in the pump-around loop, such that one heat exchanger maybe cleaned and/or serviced while the second heat exchanger is placedonline; or combinations thereof.

As noted hereinabove, the disclosed method comprises: introducing ahydrocarbon feed comprising an aromatic hydrocarbon, a hydrogen feedcomprising hydrogen, and a hydrogenation catalyst into a hydrogenationreactor operable with a liquid phase and a gas phase, whereby at least aportion of the aromatic hydrocarbon is hydrogenated to produce ahydrogenation product; removing a gas phase product stream comprisingthe hydrogenation product from the hydrogenation reactor; withdrawing aportion of the reactor liquid phase, subjecting at least a portion ofthe withdrawn portion of the liquid phase to heat exchange, thusproviding a reduced-temperature withdrawn portion, introducing thereduced-temperature withdrawn portion back into the hydrogenationreactor; and at least one of: (a) providing at least two heat exchangersto effect the subjecting of the withdrawn portion of the liquid phase toheat exchange, such that a first heat exchanger of the at least two heatexchangers can be online while a second heat exchanger of the at leasttwo heat exchangers is offline; (b) separating hydrogenation catalyst, adecomposition product of the hydrogenation catalyst, or both, from thewithdrawn portion of the liquid phase prior to subjecting the at least aportion of the withdrawn portion of the liquid phase to heat exchange;(c) reducing exposure of the hydrogenation catalyst to anoxygen-containing species; or (d) combinations thereof.

In embodiments, the herein-disclosed hydrogenation method furthercomprises introducing the gas phase hydrogenation product stream into afinishing hydrogenation reactor downstream of the hydrogenation reactor,whereby unconverted aromatic hydrocarbons in the gas phase hydrogenationproduct stream are hydrogenated. In embodiments, the finishing reactoris operated with a solid catalyst. In embodiments, the finishinghydrogenation reactor is operated with a fixed bed of hydrogenationcatalyst.

Description of the method of this disclosure will now be made withreference to the Figures. FIG. 1 is a schematic of a liquid phasehydrogenation system 100, according to an embodiment of this disclosure,which utilizes two heat exchangers, whereby one can be taken offline forservice or maintenance while another is placed online. In this manner,the hydrogenation system can be kept online while a heat exchanger istaken offline.

Hydrocarbon feed and hydrogen feed are introduced via hydrocarbon feedline 105 and hydrogen feed line 115, respectively. The hydrocarbon feedcomprises an aromatic hydrocarbon to be hydrogenated. In embodiments,the aromatic hydrocarbon comprises benzene and/or toluene, and thehydrogenation product comprises cyclohexane and/or methyl cyclohexanealong with hydrogen feed components. Other minor constituents may bepresent; for example, a benzene fed may comprise a small amount (e.g.,0.10 wt %) of other C6 components, in embodiments. The hydrogen feedcomprises a gas containing hydrogen. In embodiments, the hydrogen feedcomprises hydrogen, methane, ethane, propane, n-butane, and isobutene.In embodiments, the hydrogen feed comprises greater than or equal to 90,95, or 100 volume percent hydrogen. In embodiments, the hydrogen ispresent in excess of the stoichiometric amount needed to hydrogenate thearomatic hydrocarbon.

Within hydrogenation reactor 120, hydrogenation of the aromatichydrocarbon is effected in the liquid phase. The operating conditionsfor carrying out the hydrogenation of aromatic hydrocarbons tonaphthenic hydrocarbons are variable and depend mainly on the nature ofthe hydrocarbon being hydrogenated.

In the case of benzene hydrogenation, the temperature may be in therange of from about 125° C. to about 275° C., from about 170° C. toabout 230° C., from about 100° C. to about 200° C., or from about 100°C. to about 250° C. In embodiments, the temperature is low enough (e.g.,less than about 250° C.) to prevent hydrocracking of a hydrocarbon feed.The pressure is that pressure sufficient to maintain a liquid phase, andmay be in the range of from about 5 to about 100 atmospheres, from about20 to about 30 atmospheres, or from about 15 to about 30 atmospheres, inembodiments.

As noted hereinabove, the catalyst may be any suitable hydrogenationcatalyst known to those of skill in the art. In embodiments, thecatalyst comprises a metal from Group VIII of the periodic table. Inembodiments, the catalyst comprises nickel. In embodiments, thehydrogenation catalyst comprises soluble nickel species and one or morealuminum alkyls. In embodiments, the hydrogenation catalyst comprises atrialkylaluminum, nickel carboxylate, and sodium carboxylate in asaturated hydrocarbon solution.

As discussed further hereinbelow, in embodiments, the catalyst comprisesa solid support, enabling separation of the catalyst from the withdrawnliquid phase prior to heat exchange of a solids-reduced withdrawnportion. In embodiments, the catalyst support is selected from silica,alumina, carbon, and combinations thereof.

Reactor liquid phase is withdrawn from hydrogenation reactor 120 viareactor liquid phase outlet line 125. Pump 130 is operable to pumpwithdrawn reactor liquid phase from hydrogenation reactor 120 into thepump-around loop, comprising first heat exchanger 140A and second heatexchanger 140B. Withdrawn liquid phase is introduced, via first pumpoutlet line 135A into first heat exchanger 140A, in which thetemperature of the withdrawn reactor liquid phase is reduced via heatexchange with a heat exchange medium passing through first heatexchanger 140A via heat transfer line 145A. In embodiments, first heatexchanger 140A is operable to reduce the temperature of the withdrawnreactor liquid from a temperature by about 5 to 20 degrees Fahrenheit,for example, by about 10° F. (5.5° C.). Reduced-temperature withdrawnliquid phase exiting first heat exchanger 140A via first heat exchangeroutlet line 150A is returned to hydrogenation reactor 120 via recycleline 165. To maintain a desired catalyst balance within hydrogenationreactor 120, fresh hydrogenation catalyst can be introduced intohydrogenation reactor 120 via fresh catalyst inlet line 160 and recycleline 165. The catalyst flow rate via fresh catalyst inlet line 160 canbe added at a steady rate or in batch mode, and the catalyst injectionrate can vary depending on the application, for example between about 1lb/hr to 500 lb/hr.

Hydrogenation product is recovered from hydrogenation reactor 120. Inembodiments, hydrogenation product is removed as a gas from a reactorgas phase, for example via gas phase hydrogenation product outlet line155. In embodiments, hydrogenation product is removed from hydrogenationreactor 120 as a liquid. In embodiments, hydrogenation product isremoved from hydrogenation reactor 120 along with the reactor liquid viareactor liquid phase outlet line 125, and subsequently separatedtherefrom. In embodiments, the hydrogenation product comprisescyclohexane. In embodiments, the hydrogenation product in reactor liquidphase outlet line 125 comprises from about 20 to about 80, from about 30to about 70, or from about 30 to about 80 volume percent cyclohexane. Inembodiments, the hydrogenation product in line 155 comprisessubstantially pure (e.g., greater than or equal to about 97, 98, or 99volume percent) hydrogenation product.

When first heat exchanger 140A is in need of service or repair, valvesV1 and V2 are adjusted such that reactor liquid phase withdrawn viareactor liquid phase outlet line 125 is introduced, via second pumpoutlet line 135B, into second heat exchanger 140B, and bypasses firstheat exchanger 140A. In this manner, hydrogenation system 100 can remainonline while a heat exchanger is taken offline for cleaning or repair.Within second heat exchanger 140B, the temperature of the withdrawnportion of reactor liquid phase is reduced via heat transfer with a heattransfer medium in heat transfer line 145B. In embodiments, such as theembodiment of FIG. 1, first heat exchanger 140A and second heatexchanger 140B are essentially identical. For example, first and secondheat exchangers 140A and 140B may be substantially the same size, mayoperate with the same heat transfer media, or both. In embodiments, oneor both of first heat exchanger 140A and second heat exchanger 140Boperate to produce low pressure steam on the shell side thereof, whichis obtained therefrom via heat transfer lines 145A and/or 145B. Inembodiments, low pressure steam removed via heat transfer line 145Aand/or 145B comprises steam having a pressure of less than or equal toabout 160 psig (1103 kPag), 140 psig (965 kPag), or 125 psig (861 kPag),and a temperature of less than or equal to about 204° C. (400° F.).

In embodiments, such as that depicted in FIG. 2, which is a schematic ofa liquid phase hydrogenation system according to another embodiment ofthis disclosure, a method of this disclosure may utilize two disparateheat exchangers. The embodiment of FIG. 2 is equivalent to that of FIG.1, with the exception that, in the embodiment of FIG. 2, hydrogenationsystem 200 comprises first or ‘primary’ heat exchanger 240A that islarger than second or ‘swing’ heat exchanger 240B. In this embodiment,capital savings may be realized by utilizing smaller swing exchangerduring times when the primary or first heat exchanger 240A needs serviceor repair. In such embodiments, the heat throughput of the swing orsecond heat exchanger can be increased or the hydrogenation reactionrate decreased, such that adequate heat transfer is effected in secondor swing heat exchanger 240B. This may be particularly suitable forapplications in which cleaning and/or repair of the primary or firstheat exchanger takes a sufficiently short amount of time. The first heatexchanger and the second heat exchanger may be operated with coolingmedia having different compositions, different inlet temperatures, orboth. For example, in embodiments, second or swing heat exchanger 240Bmay be operated with a different cooling medium than that with whichfirst heat exchanger 240A is operated. For example, in embodiments,second or swing heat exchanger 240B is operated with cooling water orrefrigerant for the coolant so that the same duty could be achieved witha smaller bundle, while first or primary heat exchanger 240A is operatedto produce low pressure steam. In this manner, the heat throughput ofsecondary or swing heat exchanger 240B can be increased, and the liquidcooled down to a greater extent, thus achieving the same heat removalwith a lower flow rate. In this embodiment, low pressure steamgeneration may be halted while primary heat exchanger 240A is beingcleaned.

Description of a method of this disclosure will now be made withreference to FIG. 3, which is a schematic of a liquid phasehydrogenation system 300, according to an embodiment of this disclosure,which utilizes separation of solid catalyst and/or solid catalystdecomposition product(s) from a withdrawn portion of the reactor liquidphase prior to introduction of the withdrawn liquid phase into a heatexchanger of the pump-around loop. In this manner, plating out ofcatalyst metal(s) and/or of a catalyst decomposition product(s) onand/or within the heat exchanger can be prevented/minimized bypreventing/minimizing exposure of the heat exchanger to thehydrogenation catalyst and/or hydrogenation catalyst decompositionproduct(s).

In the embodiment of FIG. 3, hydrocarbon feed is introduced intohydrogenation reactor 320 via hydrocarbon feed line 305 and hydrogenfeed is introduced into hydrogenation reactor 320 via hydrogen feed line315. Within liquid phase reactor 320, hydrogenation of the aromatichydrocarbon is carried out at operating conditions as known to those ofskill in the art, and briefly outlined hereinabove.

In embodiments, reactor liquid phase comprising a slurry of solidhydrogenation catalyst and/or solid catalyst decomposition product(s) iswithdrawn via reactor liquid phase outlet line 325, and introduced intosolid/liquid separator 370. Solids (i.e., solid catalyst and/or solidcatalyst decomposition product(s)) separated from the withdrawn portionof the liquid phase in separator 370 are removed from separator 370 viaseparator solid outlet line 380. Separated catalyst can be returned tohydrogenation reactor 320 via solids return line 390. In suchembodiments, the hydrogenation catalyst can be a catalyst comprising asolid support. The catalyst support may be any suitable material knownto those of skill in the art. In embodiments, the catalyst supportcomprises silica, alumina, carbon, or a combination thereof. Inembodiments, the hydrogenation catalyst comprises nickel and one or morealuminum alkyl species and a support. The catalyst particle size may besuch that effective removal is provided in separator 370.

A portion of the separated solids can be purged via purge line 385,whereby a desired level of catalyst can be maintained withinhydrogenation reactor 320, and catalyst buildup can be avoided. Theamount of catalyst purged via purge line 385 and the amount of freshcatalyst introduced into hydrogenation reactor 320 via fresh catalystinlet line 360 can be balanced to maintain a desired catalyst inventorywithin liquid phase hydrogenation system 300. In embodiments, separator370 is operable to remove solid catalyst decomposition products from thewithdrawn portion of the liquid phase, a homogeneous catalyst isutilized, and separated solid decomposition products are removed viapurge line 385. In such embodiments, no solids return line 390 isutilized.

Withdrawn reactor liquid phase from which solids have been removed isremoved from separator 370 via separator liquid outlet line 395 andpumped via pump 330 and pump outlet line 335 into heat exchanger 340 ofthe pump-around loop. Within heat exchanger 340, the temperature of thesolids-reduced withdrawn reactor liquid phase is reduced, as noted abovewith reference to the embodiment of FIGS. 1 and 2, via heat exchangewith heat transfer medium in heat transfer line 345.Reduced-temperature, solids-reduced withdrawn liquid phase is removedfrom heat exchanger 340 via heat exchanger outlet line 350, and isreintroduced into hydrogenation reactor 320, (optionally) along withfresh catalyst introduced via fresh catalyst inlet line 360, via recycleline 365.

In alternative embodiments, as indicated via dashed line 375 in FIG. 3,separator 370 is downstream of pump 330. In such embodiments, withdrawnreactor liquid phase in reactor liquid phase outlet line 325 isintroduced via pump 330 and pump outlet line 335 into separator 370, andsolids-reduced reactor liquid phase removed from separator 370 viaseparator liquid outlet line 395 is introduced into heat exchanger 340.

Hydrogenation product is removed from reactor 320 as describedhereinabove with reference to FIGS. 1 and 2. For example, inembodiments, hydrogenation product is removed from hydrogenation reactor320 via gas phase hydrogenation product outlet line 355.

In embodiments, a method of this disclosure comprises reducing exposureof the hydrogenation catalyst to reactive species which encouragedeposit of catalyst metal on the heat exchanger of the pump-around loop.In embodiments, reducing exposure of the hydrogenation catalyst tooxygen-containing species (e.g., H₂O) comprises drying the hydrocarbonfeed, the hydrogen feed, both the hydrocarbon feed and the hydrogenfeed, or a mixed feed containing both the hydrocarbon feed and thehydrogen feed, prior to introducing same into the hydrogenation reactor,for example with dryer 475 of FIG. 4. In embodiments, reducing exposureof the hydrogenation catalyst to oxygen-containing species comprisesadding a component to the hydrocarbon feed, the hydrogen feed, both thehydrocarbon feed and the hydrogen feed, or a mixture of the hydrocarbonfeed and the hydrogen feed, wherein the component is a compound thatwill react with the oxygen-containing species. The compound can beselected from the group consisting of aluminum alkyls. In embodiments,the method comprises combining the hydrocarbon feed and the hydrogenfeed to provide a combined feed prior to introducing the combined feedinto the hydrogenation reactor. In such embodiments, adding a componentto the hydrocarbon feed, the hydrogen feed, or both, comprises addingthe component to the combined feed.

Description of such a method of this disclosure will now be made withreference to FIG. 4, which is a schematic of a liquid phasehydrogenation system 400, according to an embodiment of this disclosure,which utilizes addition of a component which reacts with reactivespecies and thus minimizes or prevents plating out of catalyst metaland/or other catalyst decomposition product(s) on surfaces of the heatexchanger of the pump-around loop. In this manner, plating out ofcatalyst metal/catalyst decomposition product(s) on the heat exchangercan be prevented/minimized by preventing/minimizing exposure of the heatexchanger to reactive species (such as oxygen-containing species,including but not limited to oxygen, water, carbon monoxide, and carbondioxide), which encourage the plating out of catalyst metal/catalystdecomposition product(s) on heat exchanger surfaces.

Hydrocarbon feed is introduced into hydrogenation reactor 420 viahydrocarbon feed line 405, and hydrogen is introduced into hydrogenationreactor 420 via hydrogen feed line 415. A component that will quicklyreact with species that undesirably encourage plating out of catalystmetal (e.g., nickel) and/or catalyst decomposition product(s) on thesurfaces within heat exchanger 440, is added from a component source 406into hydrocarbon feed line 405. In alternative embodiments, thecomponent is added from source 406 into hydrogen feed line 415. Inalternative embodiments, the component is added from source 406 intohydrocarbon feed line 405 and hydrogen feed line 415. In alternativeembodiments, hydrocarbon feed and hydrogen feed are combined prior tointroduction into hydrogenation reactor 420. In such embodiments, thesource of the component 406 is configured and the method operated suchthat the component can be introduced into the combinedhydrocarbon/hydrogen feed line prior to introduction into hydrogenationreactor 420. In embodiments, the source of the component is configuredand the method operated such that the component can be introduceddirectly into hydrogenation reactor 420.

The component added to the reactor feed or the hydrogenation reactor toreduce plating out of catalyst metal(s) and/or catalyst decompositionproduct(s) on the surfaces of heat exchanger 440 of the pump-around loopmay comprise any species known to those of skill in the art to quicklyreact with impurities known to encourage the plating out of catalystmetal/catalyst decomposition product(s) on the surface(s) of heatexchanger 440. In embodiments, the component is a species that quicklyreacts with oxygen-containing species, which are known to encourageplating out of catalyst metal(s) on the surfaces of heat exchanger 440.Such component may react with oxygen-containing species, including butnot limited to, oxygen, water, carbon monoxide, and carbon dioxide. Inembodiments, the component comprises one or more aluminum alkyls. Inembodiments, the hydrocarbon comprises benzene, the catalyst comprisessoluble nickel species and at least one aluminum alkyl, and thecomponent added to the reactor feed or the reactor comprises one or morealuminum alkyls. In such embodiments, addition of one or more aluminumalkyls to the aromatic hydrocarbon (e.g., benzene) feed, the hydrogenfeed, or both, can remove or reduce the levels of oxygen-containingspecies, thus preventing the detrimental effects such oxygen-containingspecies may have on the catalyst (e.g., on a nickel catalyst) and thesubsequent plating out of catalyst metal on the surfaces of heatexchanger 440. Utilization of aluminum alkyl(s) as the component thatwill react with the oxygen-containing species may be particularlysuitable in applications wherein the hydrogenation catalyst comprisesaluminum alkyl(s), as the introduction of additional aluminum alkyl(s)is not expected to undesirably influence the overall reaction.

In embodiments, the component added to reduce exposure of thehydrogenation catalyst to oxygen-containing species is added at a molarratio of the component to oxygen-containing species of between 1:3 and3:1. In another embodiment, the specific amount can depend on the amountof oxygen and moisture in the feed.

A portion of the reactor liquid phase is withdrawn from hydrogenationreactor 420 via reactor liquid phase outlet line 425, and pumped viapump 430 and pump outlet line 435 into heat exchanger 440 of thepump-around loop. Within heat exchanger 440, the temperature of thewithdrawn reactor liquid phase is reduced as noted hereinabove withreference to FIG. 2, via heat exchanger with heat transfer medium inheat transfer line 445. Cooled reactor liquid is removed from heatexchanger 440 via heat exchanger outlet line 450, and introduced intohydrogenation reactor 420 via recycle line 465. Fresh catalyst can beintroduced into hydrogenation reactor 420 via fresh catalyst inlet line460 and recycle line 465. Hydrogenation product is removed fromhydrogenation reactor 420 as described hereinabove with reference toFIG. 2. For example, in the embodiment of FIG. 4, gaseous hydrogenationproduct is removed from hydrogenation reactor 420 via gas phasehydrogenation product outlet line 455.

The system and method of this disclosure provide for increased runlength of a hydrogenation reactor and reduction in fouling of a heatexchanger of a pump-around loop. In embodiments, run length is increasedby utilization of multiple heat exchangers, such that hydrogenation maybe continued while one of the heat exchangers is taken offline forservice or repair. In embodiments, fouling of a heat exchanger of thepump-around loop of a hydrogenation system is reduced or prevented byoperating the hydrogenation with a supported hydrogenation catalyst in aslurry, and separation of the catalyst from a withdrawn portion of thereactor liquid phase upstream of a heat exchanger of the pump-aroundloop. In embodiments, fouling of a heat exchanger of the pump-aroundloop of a hydrogenation system is reduced or prevented by separatingsolid catalyst decomposition product(s) from a withdrawn portion of thereactor liquid phase upstream of a heat exchanger of the pump-aroundloop. In embodiments, fouling of a heat exchanger of the pump-aroundloop of a hydrogenation system is reduced or prevented by removingreactive species, which encourage plating out of catalyst metal(s) onthe surfaces of the heat exchanger and/or accumulation of catalystdecomposition product(s) within the heat exchanger of the pump-aroundloop. Such reactive species may be removed via drying of the reactorfeed(s), via the addition of a component that reacts with the reactivespecies, thus removing them from the system, or both.

The herein-disclosed system and method may enable an extension of thehydrogenation run time before the system is taken offline for service(e.g., for cleaning of a heat exchanger of a pump-around loop), or mayeliminate the need for such intervals of non-production altogether. Inembodiments, the run time provided via the system and method of thisdisclosure is increased by at least 10, 20, 30, 40, 50, 60, 70, 80, 90or 100% relative to a conventional hydrogenation system or method. Inembodiments, the run time provided via the system and method of thisdisclosure is increased by a factor of 2, 2.5, or 3 relative to aconventional hydrogenation system or method. In embodiments, theherein-disclosed system and method reduce catalyst consumption.

It is envisaged that the above-described apparatus and methods may becombined, in certain applications. For example, the addition of acomponent that reacts with reactive species that promote plating out ofcatalyst component(s) on the heat exchanger may be utilized inconjunction with multiple heat exchangers, separation of supportedhydrogenation catalyst and/or solid catalyst decomposition product(s)upstream of the heat exchanger of the pump-around loop, or anycombination thereof.

ADDITIONAL DISCLOSURE

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the detailed description of the present invention.The disclosures of all patents, patent applications, and publicationscited herein are hereby incorporated by reference.

Embodiments disclosed herein include:

A: A process for liquid phase hydrogenation of an aromatic hydrocarbon,the process comprising: introducing a hydrocarbon feed comprising thearomatic hydrocarbon, a hydrogen feed comprising hydrogen, and ahydrogenation catalyst into a hydrogenation reactor operable with aliquid phase and a gas phase, whereby at least a portion of the aromatichydrocarbon is hydrogenated to produce a hydrogenation product;removing, from the hydrogenation reactor, a gas phase product streamcomprising the hydrogenation product; withdrawing, from thehydrogenation reactor, a portion of the liquid phase; subjecting atleast a portion of the withdrawn portion of the liquid phase to heatexchange, thus providing a reduced-temperature withdrawn portion;introducing the reduced-temperature withdrawn portion back into thehydrogenation reactor; and at least one of: (a) providing at least twoheat exchangers to effect the subjecting of the withdrawn portion of theliquid phase to heat exchange, such that a first heat exchanger of theat least two heat exchangers can be online while a second heat exchangerof the at least two heat exchangers is offline; (b) separating adecomposition product of the hydrogenation catalyst, the hydrogenationcatalyst, or both, from the withdrawn portion of the liquid phase priorto subjecting the at least a portion of the withdrawn portion of theliquid phase to heat exchange; and (c) reducing exposure of thehydrogenation catalyst to an oxygen-containing species.

B: A process for hydrogenation of benzene to cyclohexane, the processcomprising: introducing a benzene feed comprising benzene, a hydrogenfeed comprising hydrogen, and a hydrogenation catalyst comprising nickelinto a hydrogenation reactor operable with a liquid phase and a gasphase, whereby at least a portion of the benzene is hydrogenated toproduce cyclohexane; removing from the hydrogenation reactor a gas phaseproduct stream comprising cyclohexane; withdrawing from the liquid phasea pump-around stream from the reactor; passing at least a portion of thepump-around stream to a heat exchanger bank comprising at least a firstheat exchanger in parallel with a second heat exchanger such that thefirst heat exchanger can be online while the second heat exchanger isoffline, and vice versa; cooling the at least a portion of thepump-around stream in the heat exchanger bank to provide areduced-temperature pump-around stream; and introducing thereduced-temperature pump-around stream back into the hydrogenationreactor.

C: A process for hydrogenation of benzene to cyclohexane, the processcomprising: introducing a benzene feed comprising benzene, a hydrogenfeed comprising hydrogen, and a hydrogenation catalyst slurry comprisinga supported nickel catalyst into a hydrogenation reactor operable with aliquid phase and a gas phase, whereby at least a portion of the benzeneis hydrogenated to produce cyclohexane; removing a product streamcomprising cyclohexane from the gas phase of the hydrogenation reactor;withdrawing a pump-around stream from the liquid phase of thehydrogenation reactor, wherein the pump-around stream comprisessupported nickel catalyst; separating the supported nickel catalyst fromthe pump-around stream to produce a supported nickel catalyst stream anda substantially catalyst-free pump-around stream; passing at least aportion of the substantially catalyst-free pump-around stream to a heatexchanger; cooling the at least a portion of the substantiallycatalyst-free pump-around stream in the heat exchanger to provide areduced-temperature pump-around stream; and introducing thereduced-temperature pump-around stream and at least a portion of thesupported nickel catalyst stream back into the hydrogenation reactor.

D: A process for hydrogenation of benzene to cyclohexane, the processcomprising: treating a benzene feed comprising benzene to form a treatedbenzene feed, treating a hydrogen feed comprising hydrogen to form atreated hydrogen feed, both treating a benzene feed comprising benzeneto form a treated benzene feed and treating a hydrogen feed comprisinghydrogen to form a treated hydrogen feed, or treating a mixed feedcomprising benzene and hydrogen to form a treated mixed feed, whereintreating reduces an amount of oxygen-containing species therein, whereinthe oxygen containing species comprise carbon monoxide, carbon dioxide,oxygen, water, or a combination thereof; introducing the treated benzenefeed, the treated hydrogen feed, both the treated benzene feed and thetreated hydrogen feed, or the treated mixed feed, and a hydrogenationcatalyst comprising nickel and at least one aluminum alkyl into ahydrogenation reactor operable with a liquid phase and a gas phase,whereby at least a portion of the benzene is hydrogenated to producecyclohexane; removing a product stream comprising cyclohexane from thegas phase of the hydrogenation reactor; withdrawing a pump-around streamfrom the liquid phase of the hydrogenation reactor; passing at least aportion of the liquid phase pump-around stream to a heat exchanger;cooling the at least a portion of the liquid phase pump-around stream inthe heat exchanger to provide a reduced-temperature pump-around stream,and introducing the reduced-temperature pump-around stream back into thehydrogenation reactor.

E: A system for liquid phase hydrogenation, the system comprising: ahydrogenation reactor operable with a liquid phase and a gas phase toconvert an aromatic hydrocarbon in a hydrocarbon feed to a hydrogenationproduct by contacting the aromatic hydrocarbon with hydrogen in ahydrogen feed in the presence of a hydrogenation catalyst; a pump-aroundloop comprising a pump configured to move a withdrawn portion of theliquid phase from the hydrogenation reactor through the pump-around loopand back to the hydrogenation reactor; at least one primary heatexchanger after the pump in the pump-around loop and configured toreduce the temperature of at least a portion of the liquid phasewithdrawn from the hydrogenation reactor, thus providing areduced-temperature withdrawn portion, prior to introduction of thereduced-temperature withdrawn portion into the hydrogenation reactor;and at least one of: (a) at least one additional heat exchanger inparallel with the at least one primary heat exchanger, and configuredsuch that the at least one primary heat exchanger can be placed offlinewhile the at least one additional heat exchanger is placed online; (b) aseparator upstream of the at least one primary heat exchanger, andconfigured to separate a decomposition product of the hydrogenationcatalyst, the hydrogenation catalyst, or both from the withdrawn portionof the liquid phase; and (c) a dryer operable to dry the hydrocarbonfeed, the hydrogen feed, both the hydrocarbon feed and the hydrogenfeed, or a mixture of the hydrocarbon feed and the hydrogen feed; asource of a component that will react with an oxygen-containing speciesin the hydrocarbon feed, the hydrogen feed, or both; or both the dryerand the source of the component.

Each of embodiments A, B, C, D, and E may have one or more of thefollowing additional elements: Element 1: wherein the aromatichydrocarbon comprises benzene and the hydrogenation product comprisescyclohexane. Element 2: wherein the hydrogenation catalyst comprisesnickel, and at least one aluminum alkyl. Element 3: wherein the firstheat exchanger and the second heat exchanger are substantiallyidentical, and wherein subjecting the at least a portion of thewithdrawn portion of the liquid phase to heat exchange produces a lowpressure steam product. Element 4: further comprising operating with oneof the at least two heat exchangers offline in order to remove acatalyst decomposition product therefrom. Element 5: wherein the firstheat exchanger is larger than the second heat exchanger. Element 6:wherein the first heat exchanger operates with a first cooling mediumand the second heat exchanger operates with a second cooling medium,wherein the first cooling medium and the second cooling medium havedifferent compositions, the first heat exchanger and the second heatexchanger have different inlet temperatures, or both. Element 7: furthercomprising operating with the first heat exchanger offline in order toremove a catalyst decomposition product therefrom. Element 8: whereinthe first cooling medium of the first heat exchanger is a boiler feedwater stream and a low pressure steam is produced therein, and whereinthe second cooling medium is selected from the group consisting ofcooling water and refrigerants. Element 9: wherein the hydrogenationcatalyst is introduced as a liquid phase catalyst, as a slurrycomprising a solid catalyst, or both. Element 10: wherein separating thedecomposition product of the hydrogenation catalyst, the hydrogenationcatalyst, or both, from the withdrawn portion of the liquid phasecomprises passing the withdrawn portion of the liquid phase through acyclone. Element 11: wherein the at least a portion of the withdrawnportion of the liquid phase is pumped into the at least one heatexchanger via a pump, and wherein the cyclone is downstream of the pumpand upstream of the heat exchange, or upstream of the pump. Element 12:wherein the hydrogenation catalyst is introduced as a slurry catalyst.Element 13: wherein separating the decomposition product of thehydrogenation catalyst, the hydrogenation catalyst, or both, from thewithdrawn portion of the liquid phase comprises passing the withdrawnportion of the liquid phase through a cyclone. Element 14: furthercomprising reintroducing at least a portion of the separatedhydrogenation catalyst into the hydrogenation reactor. Element 15:further comprising removing at least a portion of the separateddecomposition product of the hydrogenation catalyst, at least a portionof the separated hydrogenation catalyst, or both from the process.Element 16: wherein the hydrogenation catalyst further comprises asupport. Element 17: wherein the support is selected from the groupconsisting of silica, alumina, carbon, and combinations thereof. Element18: wherein reducing exposure of the hydrogenation catalyst to theoxygen-containing species comprises drying the hydrocarbon feed, thehydrogen feed, both the hydrocarbon feed and the hydrogen feed, or amixture of the hydrocarbon feed and the hydrogen feed prior tointroducing same into the hydrogenation reactor. Element 19: whereinreducing exposure of the hydrogenation catalyst to oxygen-containingspecies comprises contacting the hydrocarbon feed, the hydrogen feed,both the hydrocarbon feed and the hydrogen feed, or a mixture of thehydrocarbon feed and the hydrogen feed, with a component, wherein thecomponent is a compound that will react with the oxygen-containingspecies. Element 20: wherein the component is selected from the groupconsisting of aluminum alkyls. Element 21: wherein contacting thehydrocarbon feed, the hydrogen feed, both the hydrocarbon feed and thehydrogen feed, or a mixture of the hydrocarbon feed and the hydrogenfeed with the component comprises adding the component to the mixture.Element 22: wherein the component is selected from the group consistingof aluminum alkyls. Element 23: wherein the second heat exchanger isonline and the first heat exchanger is offline, and further comprisingservicing the first heat exchanger to remove a catalyst decompositionproduct therefrom. Element 24: wherein the first heat exchanger and thesecond heat exchanger are about the same size, and wherein the firstheat exchanger and the second heat exchanger produce low pressure steamwhen cooling the at least a portion of the pump-around stream. Element25: wherein the first heat exchanger and the second heat exchanger arenot about the same size, wherein the first heat exchanger is larger andproduces low pressure steam when cooling the at least a portion of thepump-around stream, and wherein the second heat exchanger is smaller andis cooled with cooling water or a refrigerated liquid. Element 26:wherein the treating comprises drying. Element 27: wherein the treatingcomprises the addition of at least one aluminum alkyl. Element 28:wherein the at least one primary heat exchanger is configured to producelow pressure steam. Element 29: wherein the at least one primary heatexchanger and the at least one additional heat exchanger aresubstantially identical. Element 30: wherein the at least one primaryheat exchanger is larger than the at least one additional heatexchanger. Element 31: wherein the separator comprises a cycloneupstream or downstream of the pump. Element 32: wherein the cyclone isdownstream of the pump. Element 33: wherein the hydrogenation catalystfurther comprises a support. Element 34: wherein the support is selectedfrom the group consisting of silica, alumina, carbon, and combinationsthereof. Element 35: further comprising a recycle line whereby at leasta portion of the separated hydrogenation catalyst can be reintroducedinto the hydrogenation reactor. Element 36: further comprising a linevia which at least a portion of the separated hydrogenation catalyst canbe purged. Element 37: comprising the dryer. Element 38: comprising thesource of the component. Element 39: wherein the component is selectedfrom the group consisting of aluminum alkyls. Element 40: furthercomprising piping whereby the hydrocarbon feed and the hydrogen feed canbe combined to provide a combined feed prior to introduction of thecombined feed into the hydrogenation reactor. Element 41: furthercomprising piping whereby the component can be added from the source ofthe component to the combined feed.

While embodiments of the disclosure have been shown and described,modifications thereof can be made without departing from the spirit andteachings of the invention. The embodiments and examples describedherein are exemplary only, and are not intended to be limiting. Manyvariations and modifications of the invention disclosed herein arepossible and are within the scope of the invention.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R_(l), and an upperlimit, R_(u), is disclosed, any number falling within the range isspecifically disclosed. In particular, the following numbers within therange are specifically disclosed: R=R_(l)+k* (R_(u)−R_(l)), wherein k isa variable ranging from 1 percent to 100 percent with a 1 percentincrement, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5percent, . . . 50 percent, 51 percent, 52 percent . . . 95 percent, 96percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover,any numerical range defined by two R numbers as defined in the above isalso specifically disclosed. Use of the term “optionally” with respectto any element of a claim means that the element is required, oralternatively, the element is not required, both alternatives beingwithin the scope of the claim. Use of broader terms such as comprises,includes, and having should be understood to provide support fornarrower terms such as consisting of, consisting essentially of, andcomprised substantially of.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the detailed description of the present invention.The disclosures of all patents, patent applications, and publicationscited herein are hereby incorporated by reference.

1. A process for liquid phase hydrogenation of an aromatic hydrocarbon,the process comprising: introducing a hydrocarbon feed comprising thearomatic hydrocarbon, a hydrogen feed comprising hydrogen, and ahydrogenation catalyst into a hydrogenation reactor operable with aliquid phase and a gas phase, whereby at least a portion of the aromatichydrocarbon is hydrogenated to produce a hydrogenation product;removing, from the hydrogenation reactor, a gas phase product streamcomprising the hydrogenation product; withdrawing, from thehydrogenation reactor, a portion of the liquid phase; subjecting atleast a portion of the withdrawn portion of the liquid phase to heatexchange, thus providing a reduced-temperature withdrawn portion;introducing the reduced-temperature withdrawn portion back into thehydrogenation reactor; providing at least two heat exchangers to effectthe subjecting of the withdrawn portion of the liquid phase to heatexchange, such that a first heat exchanger of the at least two heatexchangers can be online while a second heat exchanger of the at leasttwo heat exchangers is offline; and (a) separating a decompositionproduct of the hydrogenation catalyst, the hydrogenation catalyst, orboth, from the withdrawn portion of the liquid phase prior to subjectingthe at least a portion of the withdrawn portion of the liquid phase toheat exchange; (b) reducing exposure of the hydrogenation catalyst to anoxygen-containing species; or (c) both (a) and (b).
 2. The process ofclaim 1, wherein the aromatic hydrocarbon comprises benzene and thehydrogenation product comprises cyclohexane; wherein the hydrogenationcatalyst comprises nickel and at least one aluminum alkyl; or both. 3.The process of claim 1, wherein the hydrogenation catalyst is introducedas a liquid phase catalyst, as a slurry comprising a solid catalyst, orboth.
 4. The process of claim 3, comprising (a), and wherein separatingthe decomposition product of the hydrogenation catalyst, thehydrogenation catalyst, or both, from the withdrawn portion of theliquid phase comprises passing the withdrawn portion of the liquid phasethrough a cyclone.
 5. The process of claim 4, wherein the at least aportion of the withdrawn portion of the liquid phase is pumped into theat least one heat exchanger via a pump, and wherein the cyclone isdownstream of the pump and upstream of the heat exchange or upstream ofthe pump.
 6. The process of claim 3, wherein the hydrogenation catalystis introduced as a Slurry catalyst.
 7. (canceled)
 8. The process ofclaim 4 further comprising reintroducing at least a portion of theseparated hydrogenation catalyst into the hydrogenation reactor.
 9. Theprocess of claim 1, comprising and wherein reducing exposure of thehydrogenation catalyst to the oxygen-containing species comprises dryingthe hydrocarbon feed, the hydrogen feed, both the hydrocarbon feed andthe hydrogen feed, or a mixture of the hydrocarbon feed and the hydrogenfeed prior to introducing same into the hydrogenation reactor.
 10. Theprocess of claim 1, comprising (b), and wherein reducing exposure of thehydrogenation catalyst to oxygen-containing species comprises contactingthe hydrocarbon feed, the hydrogen feed, both the hydrocarbon feed andthe hydrogen feed, or a mixture of the hydrocarbon feed and the hydrogenfeed, with a component, wherein the component is a compound that willreact with the oxygen-containing species. 11.-15. (canceled)
 16. Aprocess for hydrogenation of benzene to cyclohexane, the processcomprising: introducing a benzene feed comprising benzene, a hydrogenfeed comprising hydrogen, and a hydrogenation catalyst comprising nickelinto a hydrogenation reactor operable with a liquid phase and a gasphase, whereby at least a portion of the benzene is hydrogenated toproduce cyclohexane; removing from the hydrogenation reactor a gas phaseproduct stream comprising cyclohexane; withdrawing from the liquid phasea pump-around stream from the reactor; passing at least a portion of thepump-around stream to a heat exchanger bank comprising at least a firstheat exchanger in parallel with a second heat exchanger such that thefirst heat exchanger can be online while the second heat exchanger isoffline, and vice versa; cooling the at least a portion of thepump-around stream in the heat exchanger hank to provide areduced-temperature pump-around stream; introducing thereduced-temperature pump-around stream back into the hydrogenationreactor; and (a) separating a decomposition product of the hydrogenationcatalyst, the hydrogenation catalyst, or both, from the pump aroundsteam prior to passing the at least a portion of the pump around streamto the heat exchange bank; (b) reducing exposure of the hydrogenationcatalyst to an oxygen-containing species; or (c) both (a) and (b). 17.The process of claim 16: wherein the first heat exchanger and the secondheat exchanger are about the same size, and wherein the first heatexchanger and the second heat exchanger produce low pressure steam whencooling the at least a portion of the pump-around stream; or wherein thefirst heat exchanger and the second heat exchanger are not about thesame size, wherein the first heat exchanger is larger and produces lowpressure steam when cooling the at least a portion of the pump-aroundstream, and wherein the second heat exchanger is smaller and is cooledwith cooling water or a refrigerated liquid. 18.-19. (canceled)
 20. Theprocess of claim 16, comprising (b) reducing exposure of thehydrogenation catalyst to an oxygen-containing species, and wherein (b)comprises drying, adding at least one aluminum alkyl, or a combinationthereof.
 21. The process of claim 1, wherein the first heat exchangerand the second heat exchanger are substantially identical, and whereinsubjecting the at least a portion of the withdrawn portion of the liquidphase to heat exchange produces a low pressure steam product.
 22. Theprocess of claim 1 further comprising operating with one of the at leasttwo heat exchangers offline in order to remove a catalyst decompositionproduct therefrom.
 23. The process of claim 1, wherein the first heatexchanger is larger than the second heat exchanger.
 24. The process ofclaim 1, wherein the first heat exchanger operates with a first coolingmedium and the second heat exchanger operates with a second coolingmedium, wherein the first cooling medium and the second cooling mediumhave different compositions, the first heat exchanger and the secondheat exchanger have different inlet temperatures, or both.
 25. Theprocess of claim 24 further comprising operating with the first heatexchanger offline in order to remove a catalyst decomposition producttherefrom.
 26. The process of claim 25, wherein the first cooling mediumof the first heat exchanger is a boiler feed water stream and a lowpressure steam is produced therein, and wherein the second coolingmedium is selected from the group consisting of cooling water andrefrigerants.
 27. The process of claim 16, wherein the second heatexchanger is online and the first heat exchanger is offline, and furthercomprising servicing the first heat exchanger to remove a catalystdecomposition product therefrom.
 28. The process of claim 16: whereinthe first heat exchanger and the second heat exchanger are about thesame size, and wherein the first heat exchanger and the second heatexchanger produce low pressure steam when cooling the at least a portionof the pump-around stream; or wherein the first heat exchanger and thesecond heat exchanger are not about the same size, wherein the firstheat exchanger is larger and produces low pressure steam when coolingthe at least a portion of the pump-around stream, and wherein the secondheat exchanger is smaller and is cooled with cooling water or arefrigerated liquid.